Sensors including integrated circuits (ICs) that directly sense the physical properties of objects in the sensor's environment have come into widespread use in electronic equipment. These ICs are desirably in close proximity to the external environments they measure, but they should not be damaged by the mechanical and/or electrical events that an external environment can apply.
One type of such sensing is finger sensing and associated matching that have become a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. Nos. 5,963,679 and 6,259,804, assigned to the assignee of the present invention, the entire contents of which are incorporated herein by reference. The fingerprint sensor is an integrated circuit sensor that drives the user's finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate. Additional finger sensing integrated circuits and methods are disclosed in U.S. Published Patent Application No. 2005/0089202 entitled “Multi-biometric finger sensor including electric field sensing pixels and associated methods”, also assigned to the assignee of the present invention, and the entire contents of which are incorporated herein by reference.
A number of prior art references disclose various types of packaging of IC sensors. For example, U.S. Pat. No. 6,646,316 to Wu et al. discloses an optical sensor including a sensing die with bond pads on an upper surface thereof. A flexible circuit board is coupled to the bond pads, and has an opening over the sensing surface. A transparent glass layer covers the opening in the flexible circuit board. U.S. Pat. No. 6,924,496 to Manansala discloses a similar flexible circuit attachment to a fingerprint sensor, but leaves the area above the surface open.
U.S. Pat. No. 7,090,139 to Kasuga et al. discloses a smart card including a fingerprint sensor having bond pads attached to wiring film, and also including a window or opening above the sensing surface. U.S. Published Patent Application No. 2005/0139685 to Kozlay discloses a similar arrangement for a fingerprint sensor.
Some fingerprint sensors are based on thin film technology, such as disclosed in U.S. Published Application No. 2006/0050935 A1 to Bustgens et al. Other fingerprint sensors may include sensing elements on a flexible substrate, such as disclosed in U.S. Pat. No. 7,099,496 to Benkley, III. These sensors may be slightly more rugged than integrated circuit based sensors, but may have performance shortcomings.
U.S. Published Patent Application No. 2005/0031174 A1 to Ryhanen et al. discloses a flexible circuit board covering an ASIC for capacitive electrode fingerprint sensing, and wherein the sensing electrodes are on the surface of the flexible substrate and covered with a thin protective polymer layer. In some embodiments, the sensor may wrap the flexible circuit around to the back side of the ASIC for attachment to a circuit board in a ball grid form.
U.S. Pat. No. 5,887,343, assigned to the assignee of the present invention, discloses an embodiment of a fingerprint sensor package that includes a transparent layer over the finger sensing area of a finger sensing IC. A chip carrier, having an opening for the sensing area, is coupled, either capacitively or electrically, to the bond pads on the IC via peripheral regions of the transparent layer.
U.S. Pat. No. 6,392,143 to Koshio discloses a flexible finger sensing IC mounted onto a flexible substrate. The finger sensing IC has aluminum wires coupled to external package wiring. The finger sensing IC may be mounted onto an external curved surface such as a pipe, ballpoint pen, etc.
U.S. Published Patent Application No. 2005/0263836 to Okada et al. discloses a finger sensing package having an LSI chip for reading a fingerprint, a substrate having external connection terminals and to which the LSI chip is fixed, and a chip fixing mechanism for fixing the LSI chip in a state where the LSI chip is deformed so as to form a curved surface. The finger sensing area is flexible, such as to be formed into a curved shape, but the package is mounted on a flat surface.
U.S. Published Patent Application No. 2003/0215117 to Hata discloses a fingerprint sensing apparatus with a flexible finger sensing IC mounted on a substrate. The fingerprint sensing IC is connected to adjacent electronics, such as LED chips, which are also mounted externally on the substrate. This finger sensing apparatus is mounted on a wiring substrate.
Finger sensing ICs are currently used in portable electronic devices. Although the finger sensing IC may be exposed to the external environment, the finger sensing IC is typically installed and coupled to an underlying internal printed circuit board (PCB) of the electronic device. Accordingly, manufacturers of the electronic device typically allocate limited space on the internal PCB to mount the finger sensing IC. The housing of the portable electronic device typically would also include an opening large enough to provide user access to the finger sensing surface of the finger sensing IC. In other words, a typical portable electronic device may sacrifice limited real estate on the internal PCB.